1. Field of the Invention
The present invention relates to a process for the preparation of a phosphoric monoester through the phosphorylation of an organic hydroxyl compound. More particularly, the present invention relates to a process for the preparation of a phosphoric monoester which can easily provide a phosphoric ester mixture having a high phosphoric monoester purity, a reduced orthophosphoric acid content and good odor.
2. Description of the Related Art
Phosphoric esters of organic hydroxyl compounds are used in a wide field as a detergent, a textile treating agent, an emulsifying agent, a rust inhibiter, a liquid ion exchanger and a medicament.
Although the reaction of an organic hydroxyl compound with phosphorus pentaoxide has been known as an industrial process for the preparation of phosphoric esters in the prior art, the product of the reaction comprises mainly a nearly equimolar mixture of a phosphoric monoester represented by the following formula (A) and a phosphoric diester represented by the following general formula (B) (hereinafter, this mixture is referred to as "sesquiphosphate"): ##STR1## wherein R represents a linear or branched alkyl or alkenyl group having 6 to 30 carbon atoms.
There are great differences in properties between a phosphoric monoester and a phosphoric diester. To give an explanation about, e.g., alkali metal salts and alkanolamine salts of long-chain alkyl phosphates, phosphoric monoester salts are soluble in water, excellent in foaming power and detergency, less toxic and lowly irritant to the skin to be useful as an excellent detergent, while phosphoric diester salts are little soluble in water and exhibit little foaming power or rather have defoaming properties, and accordingly they can not be used as high foaming detergents. Therefore, when sesquiphosphate salts are employed, the above performances inherent in phosphoric monoester salts can not be exhibited, and, therefore, sesquiphosphate salts are unusable as substitutes for phosphoric monoester salts.
Under these circumstances, the development of a process by which a phosphoric ester mixture having a high phosphoric monoester content can be prepared on an industrial scale safely and easily has been eagerly expected and the following processes have been reported to answer this expectation:
(1) a process which comprises reacting an organic hydroxyl compound with phosphorus oxychloride and hydrolyzing the obtained monoalkyl phosphorodichloridate; PA1 (2) a process which comprises adding water to an organic hydroxyl compound and thereafter adding phosphorus pentaoxide to the obtained mixture to conduct phosphorylation with the amount of water preliminarily added being 0.5 to 3 mol per mol of phosphorus pentaoxide; PA1 (3) a process which comprises reacting an organic hydroxyl compound with orthophosphoric acid and phosphorus pentaoxide; PA1 (4) a process which comprises reacting an organic hydroxyl compound with a condensed phosphoric acid (polyphosphoric acid); PA1 (5) a process which comprises reacting an organic hydroxyl compound with phosphorus pentaoxide in the presence of water while blowing steam into the reaction system; and PA1 (6) a process which comprises reacting an organic hydroxyl compound with a phosphorylating agent mixture comprising phosphorus pentaoxide, phosphoric acid and a polyphosphoric acid under such a condition that phosphoric acid components are excess, adding an organic hydroxyl compound to the obtained reaction mixture to make up to a stoichiometric amount and conducting further phosphorylation see U.S. Pat. No. 4,350,645 (published on Sep. 21, 1982, assignee: Kao Corporation)!. PA1 (1) a first step of reacting an organic hydroxyl compound with polyphosphoric acid under such conditions that the ratio, as defined by formula (1), has a value exceeding 3.2, and PA1 (2) a second step of adding phosphorus pentaoxide in such an amount that the ratio, as defined by formula (1), has a value in the range of from 2.8 to 3.2: ##EQU2##
However, these processes have respective disadvantages as will now be described, being unsatisfactory as industrial processes for the preparation of phosphoric ester mixtures.
The process (1) gives hydrogen chloride as a by-product to be significantly problematic in the corrosion of equipment and the disposal of hydrochloric acid. Further, this process involves the formation of an alkyl chloride as a by-product, so that it is difficult to enhance the phosphoric monoester content of the reaction product.
According to the processes (2) and (3), the ratio of the phosphoric monoester to the phosphoric diester in the reaction product can be enhanced by increasing the amount of water or orthophosphoric acid used. However, the use of a large amount of water or orthophosphoric acid remarkably lowers the degree of conversion of phosphorus to give a remarkably increased amount of orthophosphoric acid. The contamination of the product with a large amount of orthophosphoric acid has undesirable influence on some fields, so that the use field of the product is limited.
According to the process (4), a phosphoric monoester can be prepared selectively. However, the process (4) as well as the processes (2) and (3) gives a large amount of orthophosphoric acid as a by-product. To decrease the amount of orthophosphoric acid formed as a by-product according to the process (4), it is necessary to use a polyphosphoric acid having an extremely high degree of condensation. However, such a polyphosphoric acid is in the form of a high-viscosity gel, which necessitates the use of an industrially special reactor and makes the manufacture difficult.
According to the process (5), the ratio of the phosphoric monoester to the phosphoric diester is enhanced by blowing steam into the reaction system. However, the blowing of steam into the reaction system increases the amount of orthophosphoric acid formed. As described above, the contamination of the product with a large amount of orthophosphoric acid has undesirable influence on some fields, so that the use field of the product is limited.
According to the process (6), only a small amount of an organic hydroxyl compound is present in the reaction system in the early stages of the reaction, so that the phosphoric monoester/phosphoric diester ratio of the reaction product is enhanced. However, when the amount of an organic hydroxyl compound used in the early stages lies within a certain range, the reaction product takes the form of a high-viscosity gel to necessitate the use of an industrially special reactor. In some cases according to the process (6), additionally, the decomposition of the phosphoric monoester formed proceeds, so that the yield of the phosphoric monoester is lowered with an increase in the orthophosphoric acid content of the reaction product. The increase in the orthophosphoric acid content has undesirable influence on some fields, so that the use field of the resulting product is limited.